WL#9644: Enable event_scheduler by default

The event scheduler is OFF by default, which means that not many users will be
using it.
There are a number of features possible in the SYS schema that are not currently
done (such as kill idle transactions) because of this.
This WL will change the default to event_scheduler=ON.

Functional Requirement:
- Event scheduler should be ON by default when the server starts.